1. Field of the Invention
The invention relates to a portable appliance for the subcutaneous or intradermal injection of a liquid formulation of an active principle or ingredient.
2. Description
There has for some time past clearly been a need for small, compact and portable injection appliances which can be worn on a suitable part of the body and which provide a preferably subcutaneous release of accurately defined quantities of active principles into the body over prolonged periods of time. Various devices of this kind having considerable advantages over the conventional subcutaneous syringe are already known. In conventional subcutaneous injection a so-called bolus of an active principle is introduced into the body and must be gradually absorbed and distributed therein. Distribution depends to a considerable extent upon the physiological circumstances of the individual being treated and is therefore uncontrollable. The advantage of appliances which release an active principle continuously over a prolonged period of time is that administration can be accurately controlled to suit the body's requirements. Indeed, it is possible for phases of release to alternate with phases of non-release. A physiologically adapted release of this kind is advantageous more particularly in the case of highly active agents such as insulin, interferon or the like.
Conventionally, known appliances of this kind have a vessel which contains the active principle and with which an injection needle communicates. Pump means discharge the contents of the vessel into the body of a patient over a predetermined period of time. DE No. 3 121 888 (U.S. Pat. No. 4,601,707) discloses an example of such an appliance. It has a supply vessel in the form of a hose which a clockwork-driven squeezing roller empties through an injection needle connected to the end of the hose. The needle is introduced into the tissue some distance away from the appliance. The appliance can be worn or carried on the wrist like a wrist watch. An appliance of a different kind disclosed in U.S. Pat. No. 4,552,561 can be stuck to the skin and carries the injection needle on its underside so that the place where the needle penetrates the skin is covered while the appliance is in use. This appliance also needs the needle to pierce the tissue. It is more particularly the piercing of the tissue with the needle that is problematic in the case of conventional subcutaneous bolus injections and in the case of the more recent subcutaneous injection appliances hereinbefore described. People who are not experts in medicine are usually insufficiently practised to place such a needle correctly and they suffer from a completely justified fear of the likely pain.